Removal Of Toxic Cr Research Articles

Removal of toxic Cr(VI) from aqueous medium with effective magnetic carbon-based nanocomposites.

Cr(VI), which has toxic effects, is a heavy metal and it must be removed from the environment due to the various damages it causes. In this study, the removal of Cr(VI) pollutants from aqueous solutions with Fe3O4-based materials using a batch adsorption technique was investigated. Magnetically modified graphene nanoplatelet (GNP)-based nanocomposites were prepared and their structures were characterized by FTIR, XRD, SEM, BET, and TGA techniques. The effects of various physicochemical parameters such as adsorbent dose, contact time, initial Cr(VI) solution concentration, pH, and the presence of coexisting ions (NaCl) on the adsorption process were investigated. Accordingly, the optimum conditions for Cr(VI) removal were determined. Nonlinear Langmuir, Freundlich, and Temkin isotherm models and pseudo-first-order, pseudo-second-order, and Bangham kinetic models were used to investigate the adsorption mechanism. The experimental data relatively fit the second-order kinetic model and the Freundlich isotherm model. The maximum adsorption capacities for pure Fe3O4 (Fe:GNP 1:0), Fe:GNP (2:1), and Fe:GNP (1:1) nanocomposite materials at 298 K and pH of approximately 5 were obtained as 12.71 mg/g, 27.03 mg/g, and 62.27 mg/g, respectively. This result showed that Cr(VI) removal increased as the amount of GNP in the composite material increased. Generally, the results confirmed that magnetically modified GNP-based adsorbents are functional and promising materials that can be used for the removal of pollutants such as Cr(VI) from aqueous media.

Functionalized Titanium-Based MOF for Cr(VI) Removal from Wastewater.

The removal of toxic Cr(VI) is a hot topic in the environmental remediation field. In this work, a Ti-based metal-organic framework (MOF) (MIL-125(Ti)-NH2) was successfully functionalized by introducing amidoxime groups for the first time. The functionalized material (MIL-125(Ti)-AO) exhibited excellent Cr(VI) adsorption performance with a maximum adsorption capacity of 271 mg·g-1 according to Langmuir fitting. More importantly, during the adsorption process, Cr(VI) could be simultaneously reduced to less toxic Cr(III) species, and the residual concentration of chromium in the treated water was below the drinking water limit (0.05 mg·L-1) recommended by WHO. The effects of initial pH, contact time, and the initial concentration of Cr(VI) and the presence of competitive ions on the Cr(VI) adsorption performance of MIL-125(Ti)-AO were systematically investigated. The excellent Cr(VI) removal performance of MIL-125(Ti)-AO was attributed to the synergistic effects of simultaneous adsorption of Cr(VI) and Cr(III) by a [Ti-O] bond when Cr(VI) was reduced to Cr(III) by amidoxime groups.

Immobilization of ZnIn2S4 on sodium alginate foam for efficient hexavalent chromium removal

Photocatalytic technology has been extensively studied in the removal of toxic Cr(VI) from wastewater. However, common powdery photocatalysts suffer from poor recyclability and secondly pollution. Herein, the zinc indium sulfide (ZnIn2S4) particles were integrated onto the sodium alginate foam(SA) matrix through a facile way to obtain foam-shape catalyst. Diverse characterization techniques including X-ray diffraction(XRD), Fourier transform infrared(FT-IR), scanning electron microscope(SEM) and X-ray photoelectron spectroscopy(XPS) were employed to reveal the composite compositions, organic-inorganic interface interactions, mechanical property, and pore morphology of the foams. Results demonstrated that the ZnIn2S4 crystals wrapped on SA skeleton tightly and constructed a flower-like structure. As-prepared hybrid foam with lamellar structure showed great potential in Cr(VI) treatment due to the presence of macropores and highly available active sites. A maximum Cr(VI) photoreduction efficiency of 93 % were observed over the optimal sample of ZS-1 (with a ZnIn2S4:SA mass ratio of 1:1) under visible irradiation. When tested with mixed pollutants (Cr(VI)/dyes), the ZS-1 sample displayed an enhanced removal efficiency of 98 % for Cr(VI) and 100 % for Rhodamine B(RhB). Moreover, the composite maintained prominent photocatalytic performance and a relatively integral 3D structure scaffold after continuous six runs, revealing its superior reusability and durability.

Rapid reduction of Cr(VI) with plant leaves: Implications for ex-situ phytoremediation of chromium-polluted waters in cold region

Removal of toxic Cr(VI) with waste biomass via adsorption is considered an eco-friendly technology for remediation of chromium-polluted water. However, the roles of dissolved organic matter (DOM) released from waste biomass are often neglected in the overall Cr(VI) depletion. In this study, the utilization of plant leaves (PLs), eco-friendly waste biomass resources, is investigated for Cr(VI) reduction. The abiotic reduction rates of Cr(VI) by 10 types of PLs in aqueous (25 °C) and frozen (−20 °C) solutions are compared. The higher efficiencies (18.3%–54.0%) of Cr(VI) depletion are achieved with most PLs at −20 °C under acidic conditions. The freeze-enhanced Cr(VI) reduction with PLs is also demonstrated in practical Cr(VI)-polluted industrial wastewater. Interestingly, unlike previous chemically modified leaves, almost no Cr(VI)/Cr(III) species is adsorbed on these original PLs surface. It is found that Cr(VI) reduction rate is determined by both the concentration and component of DOM. D-(−)-quinic acid from Neolitsea sericea (Bl.) Koidz and lignin/carboxyl-rich acyclic molecules (CRAM) are identified as the main components responsible for Cr(VI) reduction. It may provide an eco-friendly and cost-effective technology for ex-situ phytoremediation of Cr(VI)-polluted waters, especially in cold regions/season.

Diethylenetriaminepentaacetic acid–thiourea-modified magnetic chitosan for adsorption of hexavalent chromium from aqueous solutions

Chromium pollution is a serious environmental problem given that like most heavy metals, Cr tends to persist and accumulate in the environment. In this study, diethylenetriaminepentaacetic acid–thiourea-modified magnetic chitosan (DTCS-Fe3O4) was synthesized for use as an adsorbent for Cr(VI) removal from aqueous solutions. The effects of various treatment conditions on the Cr(VI) adsorption performance of DTCS-Fe3O4 composite as well as the kinetics were elucidated. Moreover, by observing the structure and morphology of DTCS-Fe3O4, the possible Cr(VI) adsorption mechanism was proposed. DTCS-Fe3O4 exhibited a maximum adsorption capacity of 321.3 ± 6.0 mg g−1. Further, the adsorption process, which followed the Langmuir model for monolayer adsorption, was predominantly governed by chemical adsorption, and could be fitted using the pseudo-second-order kinetics model. Furthermore, given its ease of preparation, low cost, and remarkable performance, it is expected that the DTCS-Fe3O4 composite would find wide practical application in the removal of toxic Cr(VI) from wastewater.

Toxic chromium treatment induce amino-assisted electrostatic adsorption for the synthesis of highly dispersed chromium catalyst

Removal of toxic Cr (VI) from aqueous solutions using silicon-based adsorbents has been widely investigated. Meanwhile, contradictory between highly dispersed active Cr species and high Cr loading over commercial Cr-based catalyst was inevitable. In this work, amino-assisted electrostatic adsorption from toxic Cr (VI) treatment was developed to prepare highly dispersed Cr oxides catalysts supported on MCM-41. The Cr loading was as high as 15 wt%, and structure characters of the catalysts were well-reserved. As a result, electrostatic adsorption and subsequent complexation from negatively charged Cr (VI) species and positively charged ammonium groups made a positive contribution to the appearance of highly dispersed mono Cr species, which gave rise to improved non-oxidative propane dehydrogenation (PDH) activity. In contrast, the agglomeration of Cr species and lower PDH activity were observed on the sample synthesized using the traditional wet impregnation method. Besides, the transformation of Cr (VI) to active Cr (III) sites over the catalyst was proved by the designed in-situ H2-TPR, ex-situ UV–vis and Raman spectra results. This procedure reflects a new avenue of green chemistry, which can recycle waste Cr adsorbents as efficient PDH catalysts.

Effect of pH on hexavalent chromium removal driven by henna (Lawsonia inermis) fermentation

pH is significant to fermentation, species distribution of chromium, and removal of toxic Cr(VI). At pH 5, 7, 9, and 11, the coupled process of Cr(VI) removal driven by henna fermentation was investigated. In despite of the low adsorption capacity of Cr(VI) on henna biomass (4.10–2.73 mg/g), the fermentation process benefited Cr(VI) reductive removal by providing bio-available electron donors (volatile fatty acids, VFAs) and mediator (lawsone). During the 1st batch (days 1–4), the generation of sufficient electron donors ensured a nearly complete Cr(VI) removal (>99 %), and the removal rate was slightly higher at pH 9. During the 2nd (days 5–13) and 3rd (days 14–23) batches, the removal rate declined due to the lack of electron donors. At pH 11, although more VFAs and lawsone were produced, the removal of total chromium and the immobilization of Cr(III) were lowest. This was ascribed to the formation of more soluble organic-Cr(III) complex rather than Cr(OH)3 precipitation, thereby increasing the solubility of Cr(III). Furthermore, X-ray photoelectron spectroscopic analysis showed that it was more suitable for Cr(III) immobilization on henna biomass at pH 9 (64.4 %) than at pH 11 (54 %). Therefore, mild pH 9 is optimum for Cr(VI) removal in henna fermentation-driven system, in which the specific removal rate of 23.7 mg Cr(VI) / (g d) was achieved.

New Bioadsorbent Derived from Winemaking Waste Cluster Stalks: Application to the Removal of Toxic Cr(VI) from Liquid Effluents

A winemaking waste was used as a precursor of activated carbon used for the removal of hazardous Cr(VI) from solutions. The preparation process consisted of a hydrothermal process and a chemical activation of the resulting product, with KOH. The adsorption results show that the adsorption of Cr(VI) on the obtained activated carbon is strongly dependent on the stirring speed applied to the carbon/solution mixture, pH of the solution, and temperature. The equilibrium isotherm was well fitted to the Langmuir Type-II equation, whereas the kinetic can be described by the pseudo-second-order kinetic model. Thermodynamic studies revealed that Cr(VI) adsorption was an exothermic and spontaneous process. Finally, desorption experiments showed that Cr(VI) was effectively desorbed using hydrazine sulfate solutions, and, at the same time, the element was reduced to the less hazardous Cr(III) oxidation state.

Exploration of different adsorption performance and mechanisms of core-shell Fe3O4@Ce-Zr oxide composites for Cr(VI) and Sb(III)

Removal of toxic Cr(VI) and Sb(III) from wastewater is crucial owing to their potential hazard to the environment and human health. In this work, a novel magnetic composite, core-shell Fe3O4@Ce-Zr binary oxide (Mag@Ce-Zr), was synthesized by a simple and eco-friendly co-precipitation method to remove Cr(VI) and Sb(III). The synthetic Mag@Ce-Zr composites exhibited superior magnetic separation (saturation magnetization value was 43.8 emu/g), great maximum adsorption capacities toward Cr(VI) and Sb(III) (66.7 mg/g for Cr(VI) and 365.2 mg/g for Sb(III)) and remarkable regeneration and reusability property. The adsorption mechanisms of negatively charged Cr(VI) oxyanions involved electrostatic attraction and the formation of Ce/Zr-O-Cr complexes. However, Sb(III) was adsorbed mainly through surface complexation with abundant hydroxyl groups to form Ce/Zr-O-Sb complexes. More importantly, based on X-ray photoelectron spectroscopy analysis, partial Cr(VI) and Sb(III) were converted to less toxic Cr(III) and Sb(V) by the core Fe(II) and shell Ce(IV) of Mag@Ce-Zr through electron transfer during adsorption process. Results revealed that the Mag@Ce-Zr composites displayed greater potential in the removal of Sb(III) from wastewater owing to its higher affinity with antimony species.

Efficient capture of Cr(VI) by carbon hollow fibers with window-like structure.

Removal of toxic Cr(VI) from contaminated water is significant for environmental protection. High efficient adsorbents with outstanding adsorption performance are highly demanded. Herein, we reported that window-like structured carbon hollow fibers (WL-CHF) derived from Enteromorpha prolifera could capture toxic Cr(VI) from aqueous solutions with high adsorption capacity, fast adsorption rate, and excellent recyclable performance. The excellent adsorption performance could be attributed to the unique structure that combines a variety of advantages: large specific surface area, fast diffusion processes, and easy access of adsorption sites for Cr(VI). In addition, the adsorption process was fitted well with pseudo-second-order model and Langmuir isotherm model. The potential mechanism on Cr(VI) removal includes reduction-cation exchange and electrostatic interaction with surface oxygen-containing functional groups. This study highlights new opportunities for designing adsorbents for Cr(VI) removal from Cr-polluted water.

Removal of toxic pollutants from aqueous media using poly (vinyl imidazole) crosslinked chitosan synthesised through microwave assisted technique

Water contamination owing to the presence of toxic organic chemicals/heavy metals are considered to be one of the serious global environmental issues. Various advanced polymeric materials have been developed and used for the separation/removal of these contaminants. To consider the afore-mentioned problem, recently in authors’ laboratory, an efficient biopolymeric adsorbent has been prepared using poly (vinyl imidazole) crosslinked chitosan (cl-Ch-pVI) through a simple microwave-assisted free radical polymerization technique. The structural characteristics of the developed hydrogel have been studied in details. The copolymer cl-Ch-pVI reveals excellent gel characteristics, demonstrates superior efficiency towards removal of toxic Cr(VI) from aqueous solution. Moreover, the copolymer also shows outstanding adsorption capacity to remediation of organic dye reactive black 5 (RB5), which manifests the potential application of synthesised copolymer in wastewater treatment.

Characterization of Penicillium oxalicum SL2 isolated from indoor air and its application to the removal of hexavalent chromium.

Removal of toxic Cr(VI) by microbial reduction is a promising approach to reducing its ecotoxicological impact. To develop bioremediation technologies, many studies have evaluated the application of microorganisms isolated from Cr(VI)-contaminated sites. Nonetheless, little attention has been given to microbes from the environments without a history of Cr(VI) contamination. In this study, we aimed to characterize the Cr(VI) tolerance and removal abilities of a filamentous fungus strain, SL2, isolated from indoor air. Based on phenotypic characterization and rDNA sequence analysis, SL2 was identified as Penicillium oxalicum, a species that has not been extensively studied regarding Cr(VI) tolerance and reduction abilities. SL2 showed high tolerance to Cr(VI) on solid and in liquid media, facilitating its application to Cr(VI)-contaminated environments. Growth curves of SL2 in the presence of 0, 100, 400, or 1000 mg/L Cr(VI) were well simulated by the modified Gompertz model. The relative maximal colony diameter and maximal growth rate decreased as Cr(VI) concentration increased, while the lag time increased. SL2 manifested remarkable efficacy of removing Cr(VI). Mass balance analysis indicated that SL2 removed Cr(VI) by reduction, and incorporated 0.79 mg of Cr per gram of dry biomass. In electroplating wastewater, the initial rate of Cr(VI) removal was affected by the initial contaminant concentration. In conclusion, P. oxalicum SL2 represents a promising new candidate for Cr(VI) removal. Our results significantly expand the knowledge on potential application of this microorganism.

Removal of toxic Cr(VI) ions from tannery industrial wastewater using a newly designed three-phase three-dimensional electrode reactor

In this research, the wastewater samples were collected from leather tanning industry at different time intervals. The parameters like pH, electrical conductivity, temperature, turbidity, chromium and chemical oxygen demand (COD) of the samples were analyzed. A three-phase three-dimensional fluidized type electrode reactor (FTER) was newly designed for the effective removal of toxic pollutants from wastewater. The influencing parameters were optimized for the maximum removal of toxic pollutants from wastewater. The optimum condition for the present system was calculated as: contact time of 30 min, applied voltage of 3 V and the particle electrodes of 15 g. The particle electrode was characterized by using FT-IR analysis. Langmuir-Hinshelwood and pseudo-second order kinetic models were fits well with the experimental data. The results showed that the FTER can be successfully employed for the treatment of industrial wastewater.

Nanoporous carbon synthesized from grass for removal and recovery of hexavalent chromium

Nanoporous carbon structures were synthesized by pyrolysis of grass as carbon precursor. The synthesized carbon has high surface area and pore volume. The carbon products were acid functionalized and characterized by Fourier transform infrared spectroscopy, X-ray diffraction, Brunauer–Emmett–Teller, transmission electron microscopy, and Energy Dispersive X-ray microanalysis. Acid functionalized nanoporous carbon was explored for use in removal of toxic Cr(VI) ions from aqueous media. An adsorption study was done as a function of initial concentration, pH, contact time, temperature, and interfering ions. The experimental equilibrium data fits well to Langmuir isotherm model with maximum monolayer adsorption capacity of 35.335 mg/g. The results indicated that removal obeys a pseudo-second-order kinetic model, and that equilibrium was reached in 10 min. A desorption study was done using NaOH. The results of the present study imply that acid functionalized nanoporous carbon synthesized from grass is an efficient, renewable, cost-effective adsorbent material for removal of hexavalent chromium due to its faster removal rate and reusability.

Comparison of Cr(VI) removal by activated sludge and dissolved organic matter (DOM): importance of UV light

Removal of toxic Cr(VI) by activated sludge and DOM derived from activated sludge was investigated in this study. A rapid increase in TOC concentration from 50.93 to 127.40 mg L(-1) is observed during the Cr(VI) removal process by activated sludge in the pH range of 2-9. Removal efficiencies of Cr(VI) by either activated sludge or DOM greatly decreased with the increasing initial pH. Kinetics of Cr(VI) removal by activated sludge indicate that both biosorption and bioreduction are involved in the Cr(VI) removal. Cr(VI) removal by DOM is slow in dark, but it is greatly enhanced when UV light is applied. The first-order constant increases from 0.0033 (in dark) to 0.079 min(-1) (UV illumination) at pH 2.0 and 1068 mg L(-1) DOM. The enhancement of Cr(VI) reduction is due to the generation of the reactive intermediates such as O2(●-) and DOM* as DOM absorbed light energy, which plays important roles in the reduction of Cr(VI).

Cr(VI) Resistance and Removal by Indigenous Bacteria Isolated from Chromium-Contaminated Soil

The removal of toxic Cr(VI) by microorganisms is a promising approach for Cr(VI) pollution remediation. In the present study, four indigenous bacteria, named LY1, LY2, LY6, and LY7, were isolated from Cr(VI)-contaminated soil. Among the four Cr(VI)-resistant isolates, strain LY6 displayed the highest Cr(VI)-removing ability, with 100 mg/l Cr(VI) being completely removed within 144 h. It could effectively remove Cr(VI) over a wide pH range from 5.5 to 9.5, with the optimal pH of 8.5. The amount of Cr(VI) removed increased with initial Cr(VI) concentration. Data from the time-course analysis of Cr(VI) removal by strain LY6 followed first-order kinetics. Based on the 16S rRNA gene sequence, strain LY6 was identified as Pseudochrobactrum asaccharolyticum, a species that had never been reported for Cr(VI) removal before. Transmission electron microscopy and energy dispersive X-ray spectroscopy analysis further confirmed that strain LY6 could accumulate chromium within the cell while conducting Cr(VI) removal. The results suggested that the indigenous bacterial strain LY6 would be a new candidate for potential application in Cr(VI) pollution bioremediation.

Removal of Cr(VI) from aqueous solutions by magnetite nanoparticles with different sizes and crystal structure

In this work a few nanopowders of magnetite (Fe3O4) produced by different methods were used as a sorbents. Three techniques were applied to make the nanopowders: (1) gas-phase synthesis, (2) chemical precipitation from water solution, and (3) laser atomization. Using these methods, the particles with different sizes and crystal structure have been produced. The effects of the particles size and structure of nanopowders on the removal of toxic Cr(VI) from an aqueous solution imitating ground waters and wastewaters with pH = 7.4–7.8 were studied at different solution temperatures. It is shown that magnetite is effective sorbent for the removal of Cr(VI) from polluted natural waters and sewage. It is found that sorption of Cr(VI) by magnetite is irreversible and has chemisorption character, and even small rise in temperature of the solution during the sorption process sharply increases efficiency of the sorption.

Removal of toxic Cr(vi) by UV-active functionalized graphene oxide for water purification

Extraction of hazardous heavy metals like As, Hg, Cd, Cr(VI), etc. for water purification is a great challenge. Exploiting the large surface area of graphene, in the present work, we have synthesized a UV-active 2,6-diamino pyridine–reduced graphene oxide (DAP–RGO) composite to remove Cr(VI) from acidic water solution. Here, the presence of an extra pyridinic-nitrogen lone pair facilitates the removal efficiency of excess Cr(VI) [500 mg L−1 in 3 h only] over reported results so far. In addition to that, the unique advantage of this UV-active material is the enhancement of removal efficiency by 18% at a higher pH value. We believe that this study will bring forth a new class of UV-active graphene based adsorbents with remarkably high removal efficiency for toxic heavy metals from waste-water in future.

Application of ionizing radiation to environmental protection: removal of toxic Cr(VI) metal ion in industrial wastewater: preliminary study

Hexavalent chromium, a major contaminant in most wastewater sites, is a potential health threat inducing cancer to humans while trivalent chromium is an essential element for the metabolism of sugar. The radiation-induced reduction of Cr(VI) metal ion to Cr(III) by the perhydroxyl radical (HO2 • ) and carboxyl radical anion (CO2 -• ) pro- duced by continuous radiolysis of water was investigated by steady state radiolysis of O2, Ar and N2O-saturated pH 3 solutions in the presence of formate. In all cases the removed Cr(VI) was a linear function of the absorbed dose. The added formate was favorable for removing Cr(VI). Its presence protects the solution from reverse radiolytic oxi- dation of Cr(III) to Cr(VI). The measured and calculated yield of removal of Cr(VI) do agree quite well at low formate concentration but at high formate concentration the measured yield was higher than the expected. When all formate is exhausted no recovery of Cr(VI) from Cr(III) was observed in case of O2- and Ar-saturated solutions whilst in the case of N2O-saturated solutions Cr(VI) recovers. The results obtained in this study highlight the potential of this technology for industrial wastewater treatment.

Removal of Toxic Cr(VI) Ions from Aqueous Solution Using Nano-Hydroxyapatite-Based Chitin and Chitosan Hybrid Composites

In the present investigation, bio-inorganic composites composed of nano-hydroxyapatite (n-HAp) with chitin and chitosan have been prepared and used for the removal of chromium(VI) ions from aqueous solution. Such composites exhibited a higher Cr(VI) ion sorption capacity than the individual components. The sorption capacities of n-HAp, n-HAp/chitin (n-HApC) composite and n-HAp/chitosan (n-HApCs) composite were found to be 2720, 2845 and 3450 mg/kg, respectively. Batch adsorption studies were conducted to optimize various equilibrating conditions such as the contact time, pH and co-ions. The sorbents were characterized by FT-IR spectroscopy, BET and EDXA analysis. The sorption process could be fitted by both the Freundlich and Langmuir isotherm models. Standard thermodynamic parameters such as the Gibbs' free energy change, ΔG0, the standard enthalpy change, ΔH0, and the standard entropy change, ΔS0, were calculated in order to obtain an understanding of the nature of the sorption process. The kinetics of ...